An electrostatic drive type MEMS switch is a mechanical switch that makes switch between an on (ON) state and an off (OFF) state by physical contact and has a feature of having isolation, linearity and high voltage endurance that are higher than those of a semiconductor switch. In this MEMS switch, contacts are brought into contact with each other by giving a potential difference between a movable electrode and a fixed electrode and driving the actuator by the electrostatic attraction. Thereby, it becomes possible to change over the switch to the ON state.
In general, the electrostatic actuator has such an issue that a drive voltage thereof is large. It is effective to increase facing areas of the electrodes or to reduce a distance (a gap) between the electrodes in order to reduce the drive voltage without changing the electrostatic attraction (driving force) between the electrodes (between the movable electrode and the fixed electrode). The number of electrodes may be increased by arranging the electrodes in parallel with one another in order to increase the facing areas of the electrodes. However, if the number of the electrodes is increased, arrangement area (layout area) will be increased and therefore a device size will be increased. That is, the number of the electrodes and the device size are in a trade-off relation. On the other hand, in a case where the gap between the electrodes has been reduced, it becomes easy for the electrodes to come into contact with each other when operating the switch. This is because the electrodes themselves undergo a deflection by receiving the electrostatic attraction. When the contact between the electrodes occurs, energy loss caused by current leakage and malfunction caused by adhesion (stiction or sticking) between contact portions thereof occur. These factors cause a reduction in reliability. In addition, it is effective to increase rigidity of the electrodes for avoiding the contact between the electrodes. However, thickening the electrodes leads to an increase in arrangement area and therefore a trade-off occurs between low-voltage driving and the device size also in this case.
What is desired is to suppress the current leakage and the sticking caused by the contact between the electrodes and to make the gap between the electrode as narrow as possible in order to achieve the low-voltage driving without increasing the device size in the electrostatic drive type MEMS actuator (the electrostatic actuator) in this way.
PTL 1 proposes a method of providing projections on the electrodes so as to avoid the sticking when the electrodes come into contact with each other.